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Nargess Shahmanesh-Banks drives the new Lexus RX400h

With new reports from NASA suggesting that the ice cap in the arctic circle is melting at a far speedier rate than scientists had anticipated, are recent efforts to create alternative powertrains too little too late? Toyota doesn't seem to think so which is why it is promoting Lexus to be their hybrid brand. At the recent launch of the RX400h, a company spokesman promised us many more future Lexus cars with alternative powertrains.

The super-clean, silent Hybrid Synergy Drive system combines a V6 petrol engine with a front electric motor that claims to have the world's best power to weight and volume ratio

Lexus is an odd brand. In its more lucrative US market, it is valued as a premium brand, but held in second place to the German rivals Mercedes, BMW and Audi. In Europe the brand has received mixed reviews mainly due to its somewhat garish design language that hints more towards its American audience. All this, we are told, is history and the new generation of cars are designed with a company coined term 'l finess' in mind and the fruit of the facelift can be witnessed in the new GS, reviewed back in April. Now with the promise of a hydrogen option on most future models, Lexus is bound to find new glory in the future.

So back to the RX400h. It carries more or less the same body style to the RX 300, sharing the same aerodynamically-efficient design that provides excellent stability and keeps wind noise levels to a minimum. What is new is the latest state-of-the-art hybrid technology, Hybrid Synergy Drive system, as well as a few details, including a revised front grille designed to aid cooling of the and neatly integrated front fog lamps in the front bumper section.

A green silent drive

The Hybrid Synergy Drive system combines a 3.3-litre V6 petrol engine with a 167 ps (123 kW) front electric motor that has what Toyota claims to be the world's best power to weight and volume ratio, a high voltage battery and a generator. A second electric motor at the rear axle gives the vehicle an electric four-wheel drive capability – E-Four – that is automatically engaged when required.

In any journey, the system will operate in different modes in order to maintain the maximum
efficiency, with power from the engine, the electric motors or a combination of both. Whenever the vehicle comes to a halt, the engine will automatically be switched off to minimise fuel consumption.

The RX 400h can run on its electric motors alone at start-up and low to mid-range speeds, which cuts exhaust emissions to zero. In normal driving conditions, a power split device will divide output from the engine between driving the wheels and powering the generator, which in turn charges the high-voltage battery. This means the vehicle never has to be off the road to be charged.

Further energy is gained during braking or declaration with the electric motors operating as high output generators to recover kinetic energy that would usually be lost as heat and storing it as electricity in the high-voltage battery.

The system features a new, high output nickel-metal hydride 288V battery. A Hybrid Vehicle-Electronic Control Unit (HV-ECU) monitors battery recharging conditions, detects problems, performs fail-safe system management and controls the battery cooling fan.

The battery unit weighs 69kg and has an eight-cell (1.2V per cell) assembly comprising 30 in-line bus bar modules connected in series. It is divided into three sections which enables it to be located under the rear seats without compromising passenger space.

The battery and all its related components are contained in a sealed metal casing that meets the highest protection standards, shielding passengers from electromagnetic fields.
In the event of an accident, the HV-ECU immediately disconnects the battery.

Using metal rather than resin for the battery casing has allowed the battery module to be made much smaller. Compared to the previous hybrid vehicle battery pack, the overall height has been reduced by 40mm (about 22 per cent).

The metallic casing also improves cooling performance. Each of the three sections has its own cooling fan, driven by brushless motors. This permits a compact design, high efficiency and very quiet operation. Air from the cabin is brought in through three intake vents located under the front of the rear seats and flows from top to bottom between the battery modules, causing a heat exchange effect. The air exits the rear of the battery pack into an under-floor plenum, from where it is dispersed both back into the cabin and outside the vehicle. The battery is constantly recharged by the hybrid drive system, which means it never requires any charging form external power sources.

Maximum output is 279 ps (206 kW), which gives the car a top speed of 124 mph (200 km/h) and 0-100 km/h acceleration in only 7.6 seconds. Progress is relatively seamless mainly due to the Electronically Controlled Continuously Variable Transmission (E-CVT). The technology simulates a continuous variation of the transmission’s current ratio by selectively controlling the rpm of the engine, generator and electric motor. As a result, the engine and the motors operate at peak efficiency, regardless of vehicle speed. Ball bearings and low viscosity oil has reduced friction losses by around 30 per cent.

In official combined cycle driving the vehicle returns 8.09 litres/100km, which is actually on par with the very best diesel performance. In terms of exhaust emissions, the vehicle complies with Euro IV emissions standards and produces 192g/km of carbon dioxide, plus nitrogen oxides emissions are reduced to near-zero.

Safety from within

The RX 400h is the first SUV to benefit from Vehicle Dynamics Integrated Management (VDIM), a in-house system which coordinates operation of the ABS, electronic brakeforce distribution (EBD), traction control (TRC) and vehicle stability control (VSC) to maximise their performance capability.

VDIM triggers the systems when it detects the vehicle is nearing the limit of its performance, instead of them coming into play individually when that limit has been reached. This means their intervention is less obtrusive and the vehicle is kept under control more smoothly. The system also integrates the electric power steering system, adjusting steering torque to make it easier for the driver to return the vehicle to the correct course.

To improve the driver's vision through bends, SE and SE-L versions of the RX 400h are equipped with an Adaptive Front-lighting System (AFS). This swivels the headlamp beam in accordance with vehicle speed and turning angle in order to provide better illumination.

The car is equipped with a ‘by-wire’ electronically controlled brake system (ECB) and brake assist (BA). Additionally, all models are equipped with nine airbags as standard. These include a driver’s knee airbag and large capacity Thorax-Abdomen-Pelvis side airbags.

Falling in to plan

The development of the Hybrid Synergy Drive system and the RX400h fall neatly into Toyota's plan as highlighted in its Global Vision 2010, published in 2002. In this the company outlined its determination to be a leader in environmental performance as an absolute imperative. Which is why amongst other things, it is developing and popularising clean energy vehicles.

"To fulfil our own company goals as well as satisfying the different premium sector aspirations of the Lexus customer, the answer had to be hybrid technology," explains the car's chief engineer, Osamu Sadakata. "I think the use of hybrid technology will grow and spread through the market. Currently the issue is all about how to use petrol as efficiently as possible, allied to the greater horsepower you can achieve. This is what is behind the fun-to-drive aspect of the RX 400h."

Toyota is adamant to note that it is not concentrating wholeheartedly on hybrid technology at the expense of fuel cell. Sadakata explains that fuel cell technology is so complex that Toyota sees hybrid drive systems as the essential first step to its successful development. "You have to have the one before you can achieve the other," he says. "In the end, it doesn’t matter if the power source is petrol, diesel or even hydrogen, the hybrid system serves all sources as the most efficient way of using energy."

Looking to the future, he adds: "Development of fuel cell technology will continue, but ultimately circumstances will dictate whether it or petrol will be at the heart of the automobile market. The key point is how you use the limited resources we have. We still don’t know how long the world’s oil resources will last. Perhaps we will develop ever more efficient petrol engines and the oil will last longer than anticipated. This means it is impossible to put a time scale on when the shift to other power sources will become imperative."

A mid-term solution

Lexus is aiming at a wide section of premium buyers with this car. It will no doubt appeal to the ecologically aware customer as it would to those keen to save a note or two especially in the US with its rising fuel prices. Perhaps in Europe a next-generation, l finessed model will take off. Sadakata, unofficially hinted at a whole range of daringly-designed future hybrid models for both Lexus and Toyota.

It is hard to fault the car. Unless you are a driving enthusiast, it is most unlikely that you will notice some of the shortcomings in steering or really question the technology. At the end of the day, the bulk of RX400h drivers will go home after a hard day's work, put their feet up in the blissfulness knowledge that they have done their bit for the environment.